Eukaryotic cells contain nuclear as well as organelle genomes. The proper functioning of these cells and organisms requires carefully meshed expression of both genomes. The program, of which this project is a part, is directed toward understanding how these genomes relate to one another and hw they are regulated. Plastids are organelles which can differentiate into several different functional forms. In this project genes which are expressed in some cell types but not other adjacent cell types in a single organ; plastid genes which are expressed when the organism is illuminated but not when it is grown in darkness; or plastid genes which are not expressed in certain nuclear gene mutants are to be identified and their structures -- i.e., DNA sequences -- are to be determined. The immediate objective is to learn whether genes of each expression class have common elements that distinguish them from genes of other expression clones. This part of the program is aimed at increasing our knowledge of plastid gene and genome structure with the objective of understanding the possible roles of DNA structure in the regulation of chloroplast gene expression. The program is concerned with the molecular biology of gene expression in eukaryotic cells. This problem is of central importance in understanding biological processes in health and disease.